The invention relates generally to a nickel-titanium palatal expansion arch having a generally "M-shaped" configuration for simultaneous expansion of the bicuspids and expansion, rotation, torquing or intruding of the maxillary molars.
Maxillary palatal expansion appliances have been used by orthodontists for many years to create additional room for developing permanent teeth and to correct aberrations of the first molar positions. Conventional orthodontic palatal expansion devices rely on jack screws, springs and heavy helix wires to accommodate the range of movement required by the clinician. The screw-type devices require patient involvement through the treatment period in which the patient is required to adjust a jack screw which is embedded in an acrylic palatal device. Spring devices are used with coiled springs placed between a sliding rod and sheath to deliver a low extended range force to the parallel planes which begin at and are attached to a welded band device affixed to the first molars. The rods or legs parallel the teeth toward the midline. The spring rod and sheath lie in place away from the palate, becoming an interference to occlusal functions. Examples of such prior art devices are found in U.S. Pat. Nos. 4,037,324 and 3,792,529.
Each prior art appliance was painstakingly crafted each time a new patient was treated since there were no commercially standardized appliances available in any of these configurations. Thus, the clinician was involved in the time-consuming making of the appliance for each patient. Whether the clinician utilized a soldered jack screw, helix or spring device, these appliances had a very limited ability to rotate, upright, or torque malaligned or biased first molars whose proper position is all important to the orthodontic treatment objectives. In each case, additional and sometimes complex procedures were necessary to complete the molar movement.
The 3-D quad helix prior art appliance consists of a 0.036 inch wire having a "W"-shaped four loop system, laser-welded to twin vertical posts which plug into vertical lingual sheaths affixed via spot welding to the first molars. The portion of the device in contact with the cuspids and bicuspids bilaterally are called extenders and have been reduced to 0.025 inch wire for increased flexibility. If upon insertion the molar is biased in any dimension from the normal, the appliance in turn is distorted in the way it is positioned on the palate, i.e., the extenders become skewed out over the tongue when the appliance is inserted in the malpositioned molars and irritates the tongue. The appliance is fabricated in different sizes so that the clinician can select the appropriate one for the patient.
Clinicians using the 3-D expansion arch see their patients at three to four week intervals, at which time the arch can be reactivated. New force moments can be incorporated into the archwire during each visit so there would be new forces imparted to continue the movement of the teeth to a desired position. Over the course of a few weeks, the round stainless steel 3-D archwire gradually loses its ability to impart force to the teeth so that at the end of the three or four-week period, it is necessary to remove and reshape the various components.
All of the forgoing described appliances with each activation produce very high initial pressure between the maxillary teeth and palatal suture producing pain and undesirable bone responses.
Vertical post appliances remain unpopular with orthodontists because they depend on a friction grip which is immediately put under strain by any activation of the appliance. The moment that any additional force from the tongue occurs, the two forces combine to dislodge the appliance. The laser welded posts impart strain into the extenders that makes even modest adjusting predisposed to breakage.
Another prior art removable appliance used to reciprocally rotate, expand, contract, intrude and/or torque the upper molars, but does not have the capability to expand the bicuspid segment, is disclosed in U.S. Pat. No. 3,792,529.
The prior art also includes U.S. Pat. No. 4,037,324, which discloses the use of an archwire having a specific chemical composition wire which causes the archwire to return to a preset shape or length after being deformed and then heated. The mechanical memory of the wire will tend to restore the wire to a preset shape upon heating in order to level or torque malposed teeth. The prior art wires are formed of a Nitonol alloy, which is a known near-stoichiometric alloy of nickel and titanium. The alloy may also include cobalt substituted for nickel on an atom-for-atom basis so that the composition is NiTi; CO: 0.935, 0.065.